In recent years, percutaneous transluminal angioplasty has become a common procedure for use in treating obstructions (stenoses) in an artery. The most common type of this treatment involves the use of a balloon dilatation catheter that is advanced through the patient's arteries into the stenosis and then is expanded under pressure to dilate the stenosis. The dilation results in improved blood flow and circulation in the treated artery.
When angioplasty is performed on the coronary arteries, the procedure is referred to generally as percutaneous transluminal coronary angioplasty (PTCA). PTCA is a less complex alternative to coronary bypass surgery. The PTCA procedure is of relatively short duration and involves puncturing the skin and an artery (usually the femoral artery in the patient's leg) to provide access to the patient's arterial system for the PTCA balloon dilatation catheter. The PTCA catheter is manipulated and guided through the patient's arteries with the aid of a guidewire to the site of the coronary stenosis. The balloon portion of the catheter is advanced into the stenosis and then is inflated to enlarge the lumen of the artery through the stenosed region.
One method for guiding the PTCA catheter to the site of a stenosis, referred to as the over-the-wire method, is described in U.S. Pat. No. 4,545,390 to Leary, the disclosure of which is hereby incorporated by reference. The method involves the use of a slender flexible guidewire which is advanced through the patient's vascular system until its distal end is at the desired location. The direction of guidewire travel is controlled by the physician who can monitor the position of the guidewire fluoroscopically. Once the guidewire has been navigated to the desired location, the balloon dilatation catheter is advanced over the guidewire, the wire being received in a guidewire lumen that extends through the catheter. The guidewire thus simply and automatically guides the dilatation catheter directly to the intended region.
Some obstructions, due either to their location or geometry, are very difficult to access or dilate. More specifically, in some cases, the. stenosis is located within or beyond a highly tortuous artery making it very difficult to reach. In other cases, the stenosis occludes most of the artery and presents only a very narrow opening, making it very difficult to cross for proper placement of the balloon portion of the dilatation catheter. In even more complicated cases, these two conditions are combined.
Generally, a stenosis with a more narrow opening requires use of a balloon catheter having a corresponding smaller deflated cross-section, a characteristic referred to as having a low profile. In the over-the-wire systems described previously, the collapsed balloon profile has been reduced by reducing both the outside diameter of the catheter shaft in the region of the balloon and the inside diameter of its guidewire lumen. This reduced diameter permits the balloon, when evacuated and folded around the catheter body, to have a very small profile. There is a minimum limit, however, to which the guidewire lumen may be reduced, since in an over-the-wire system the physician must be able to pass the catheter over the guidewire and also withdraw the guidewire through the guidewire lumen. Thus, the guidewire lumen must always be wide enough to allow the guidewire to pass completely therethrough. A typical over-the-wire catheter has a shaft outer diameter of the order of 0.050 inches.
Alternatively, dilatation catheters having integral (non-removable) guidewires have been developed. Such catheters also are referred to as "fixed wire" catheters. Examples of such fixed guidewire catheters are described in U.S. Pat. Nos. 4,616,653; 4,573,470; 4,641,654 and 4,554,929. In these systems, the guidewire is an integral part of the catheter and is not separable from the catheter shaft. This allows a catheter of lower profile to be used because it eliminates the need to provide a guidewire lumen wide enough to allow the guidewire to pass therethrough.
The inability to separate the guidewire from the catheter in a fixed wire catheter presents some difficulties, however, because it does not allow the catheter to be exchanged for another catheter over the guidewire. The ability to perform a catheter exchange is desirable in that it allows the physician to change balloon sizes as may be desired for a number of reasons and purposes. Typically, in an over-the-wire catheter, catheter exchanges are accomplished by attaching an extension wire to the proximal end of the guidewire, removing the indwelling catheter from the patient over the extended guidewire and then sliding the new catheter along the extended guidewire to the site of the stenosis. The guidewire extension then may be detached from the guidewire. Such a procedure is described in U.S. patent application Ser. No. 07/206,008, filed June 13, 1988. In contrast, when using a fixed guidewire catheter, the catheter and guidewire necessarily are removed together, as a unit. Placement of a subsequent catheter requires that a new guidewire or catheter with an integral guidewire be inserted into the patient's arteries and re-navigated back to the stenosis thereby increasing the time required for the procedure and risk to the patient.
There is a need, therefore, for a catheter that has the low profile advantages of a fixed guidewire catheter, but which enables catheter exchanges to be performed without losing guidewire position. It is an object of the present invention to provide such a catheter arrangement.